So, a few things here...your instructor did not give you the best advice. It is critical that you know exactly what amount of weight you need to comfortably get to a negative buoyancy state at the surface...you have to be able to sink. The trick is to not have so much weight that you are having to use too much air in your BCD to counteract it. So factors you must address and take note of: Exposure protection, are you wearing a wetsuit? What thickness? This will change the weight requirements...so make a note...I would write down that "in a 3mm wetsuit in fresh water, with a full, 80 cf aluminum cylinder, with XYZ BCD, mask, fins, gloves, hood, etc...I need 16 pounds (for example) of weight to sink with my BCD fully deflated and when I exhale. In salt water, I need 18 pounds.
Each thing you add or subtract makes a difference. But the test is...how much weight do you need to sink below the surface gently when you exhale, but can stay on the surface when you inhale/breath normally. Over-weighting is a prime cause of wasted air, fatigue, poor trip, bouncing all over the water column, failure to master skills, etc.
Make sure that you study some of the many videos and articles available on properly weighting out for diving and you will have a much better experience!